[Eeglablist] ERP grand average does not reflect actual latency

[Makoto Miyakoshi]

Dear Alvin,

Sorry for belated response.
Without seeing your data, a general caution is that showing mean ERPs
without their variances can be sometimes misleading. For example, near ERP
peak latency you might expect the maximum difference and strongest
statistics, but in reality the peak are is contributed by a few datasets so
their variance is often the largest as well, which does not produce the
strongest statistics.

Well, if your case if not related to this general caution, excuse me!

Makoto

On Mon, Mar 27, 2017 at 6:30 PM, Shih-Chun Kao <shihchunkao at gmail.com>
wrote:

> Dear list,
>
> If I found a statistically significant P3 latency effect (~50ms) between
> two conditions in a within-subject design study but my grand average plot
> does not show such difference, what would be the cause for inconsistent
> results and what does such inconsistency suggest? I understand grand
> average is not the best illustration but I thought 50ms is a pretty big
> difference. Thank you!
>
> Alvin
>
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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